This invention relates to railway car draft gear and, more particularly, to railway car draft gear providing slack adjustment and cushioning. While this invention is suitable for use in a drawbar coupler or in an articulated connector and is illustrated and described herein in both applications, it may be used in other types of draft gear or couplers.
A typical railway car draft gear of this type is disclosed in U.S. Pat. No. 4,258,628. The draft gear is made up of a male connecting member adapted to be received within a cavity formed by a female connecting member, the two being joinable by a pin insertable through bores in each that become aligned when the male member is inserted into the cavity. To absorb slack and absorb shock between this pin and the bore of the male connecting member, the end of the male member is convex and is engagable in face-to-face contact with a concave surface formed in the forward face of an elastomerically supported follower. The rear face of the follower includes two slots in which two elastomeric strips are mounted, respectively, in vertical parallel alignment between opposed retaining shoulders. These strips normally protrude from their slots a distance sufficient to maintain a longitudinal space between the rear face of the follower and the vertical front face of a gravity actuated wedge, the inclined rear surface of which bears against the correspondingly inclined face of the female member at the rear of the cavity. Metal strips are bonded to the exposed faces of the elastomeric strips and bear against the front face of the wedge to establish a frictional retaining force for maintaining the wedge in a vertical disposition related to the degree of wear in the mating male, female and follower surfaces and, hence, the required slack adjustment. Due to the space maintained between the follower and wedge, horizontal and vertical pitching motions between the male and female members, such as may occur when the railway car negotiates a curve, are absorbed by total or partial compression of one or both of the elastomeric strips. Additionally, the elastomeric strips absorb and cushion longitudinal compression between the male and female members during application of buff loads. Other draft gear of this type, but without elastomeric cushioning such as that just mentioned, are disclosed in U.S. Pat. Nos. 3,716,146 and 4,336,758.
One drawback of this type of draft gear is that adjacent load bearing surfaces may come into metal-to-metal contact under certain conditions involving shifting between the male and female members, such as may occur in an articulated connector, for example, when subjected to pitching motion during curves, whether vertical or horizontal. This produces an effect similar to "spring bottoming" in coil springs, in which the spring force obtained becomes nonlinear and the spring effectively loses its resilience when it is compressed to the point that its coils come into mutual contact. This is possible with the elastomeric strips mentioned above in the event the magnitude of the pitching or buff load causes one or both strips to be compressed to the extent that the longitudinal space between the follower block and wedge becomes nonexistent. In this instance, spring bottoming effects could lead to misalignment of the wedge and a comcommitant degradation in slack adjustment since the wedge may shift in relation to the frictional retaining force exerted by the metal strips under the forces applied by the elastomeric strips during compression. The magnitude of this force, of course, is related to the total surface area of these strips, and may be insufficent to overcome the spring bottoming effects produced by severe pitching forces or buff loads. Similarly, the magnitude of this force and hence wedge misalignment could result from permanent compressive set in the elastomeric strips after being compressed substantially for a prolonged time period. This also could lead to the occurance of excess slack during application of a draft load. Such spring bottoming and compressive set effects, either singularly or in combination, could result in undesirable train run-in or run-out. Still another drawback of the particular draft gear mentioned above is that the female connector is formed from a casting which must be fitted to the draft sill. Consequently, conventional draft sills must be modified to fit properly, or else the casting must be tailored to fit with a specific draft sill, or both.